Production from ultra-low permeable gas shale reservoirs is feasible only through hydraulic fracturing stimulation. Slip along a pre-existing natural network of fractures/faults with the injection of hydraulic fluid is mostly controlled by the frictional properties of the shale. We studied the deformation characteristics of the Goldwyer shale formation at in-situ stress conditions by performing a series of multistage triaxial tests to understand compositional controls on fault slip accompanying hydraulic fracturing. The Coulomb friction coefficient is derived from the post-failure axial displacement and the angle of the final failure plane. When the clay and total organic content (TOC) of the studied shale samples are above ~40% by volume, the friction coefficient approaches a value of 0.6, while below this threshold it is higher. This change suggests a transition from a grain-bearing to a clay-bearing structure. Therefore, we can directly estimate the slip tendency of natural faults and fractures in gas shale reservoirs from their clay and TOC content.

Open-Access Online Publication: March 03, 2023